Insulator seal



April 20, 1943. K. SCHWARTZWALDER ETAL INSULATOR SEAL Filed July 5, 1941 Patented Apr. 20, 1943 INSULATOB. SEAL m Schwartzwalder and Flint, Mich., assigors to Robert W. Smith, General Motors Corporation, Detroit, Mich., a corporation of Dela- Application July 5, i9`4, Serial No. 4o1,222

4Claims. (c. 23 169 Our mvention has to do with providing a. pressure tight seal between a ceramic body and metal.

More particularly, it has to do with sealing electrodes in spark plug insulators.

In the spark plug industry today, -it is proposed to make plugs in which a glass seal between the insulator and center wire or electrode provides a. pressure tight connection by virtue of a bond which the glass forms with both the electrode and the insulator. For best results, it has been found that the metal of the electrode should have a. low coefilcient oi' expansion, and that the coeflicient oi' expansion of the glass should be as close 'as possible to that of the metal. Low coeflicient of expansion metals, w-ith which a glass seal may readily be made to bond, are usually quite expensive. In our invention we have made it possible to retain the advantages of a metal which bonds readily with a. glass seal and a less expensive metal having satisfactory properties as an electrode. We do this by making the center wire or electrode in two or more pieces, in which the metal which readily bonds with glass is Joined to the metal electrode. Only so much of the former is used as may be necessary to insure a fluid tight seal.

It is an object of our invention to provide a seal between metal and a ceramic body which is strong, gas tight and permanent. This seal is made by the use of glass as the sealing element.

More specifically, it is the principal object of our invention to eifect a seal between a spark plug insulator and its electrode by the use of glass in such a. manner that the glass reacts with and bonds to both the metal and the ceramic body or insulator. This object is achieved without impairment of the Operating efliciency of the plug.

Figure 1 of the drawing shows an insulator with the electrode and sealing material in place in the insulator before heat and pressure have been applied to complete the seal.

. Figure 2 shows the completely assembled spark lug. Referring to the drawing in detail, o indicates a spari: plug insulator made of any suitable ceramic material. Thus the insulator may be of the porcelain type long in common use or the more recently developed sintered oxide or modified sintered oxide type. The insulator is provided with a counterbore or pocket l2 which may be threaded ii' desired. A hole or longitudinal bore I 3 in the lower part of the insulator receives the center wire or electrode M. Electrode Il may be provided with a head or flange ti which rests against the shoulder formed at the juncture of longtudinal bore l3 and counterbore !2. The upper portion or terminal i8 of the center wire may be a screw which has a slightly smaller diameter than' the counterbore of the insulator. screw [8 is provided with a bore or recess 20 to receive a conductor or pilot .wire 22. Wire 22 should be of a material which has a low coeiiicient of thermal expansion such as molybdenum, tungsten, invar and the like. Pilot 22 is joined to electrode [4, as by welding, at the top of head !6 of the electrode. Electrode M is preferably made of a suitable heat resisting alloy material, such as a nickel alloy. Termnal 18 may be any good electrical conductor; we have found steel to be a satisfactory material.

A cylindrical pellet 23 of the cementing o' sealing material fits over pilot wire 22. Pellet 23 is preferably a hard glass, such as a borosilicate glass; a satisfactory glass which is commercially available is that known as Pyrex. This glass unites with both the insulator and the metal pilot wire during the sealing operation. A second pellet 24 is provided to secure terminal !8 in the insulator. Pellet 24 preferably consists of glass having a greater plasticity than glass pellet 23. A lead borosilicate glass combined with graphite or a metal has been found satisfactory for pellet 24. This glass may have the composition 50% B2O3-20% PbO-30% Si02. We may provide a filler of powdered Copper or Ticonderoga graphite. If pellet 24 is made from a mixture of glass and graphite we have found a satisfactory proportion to be glass, 30% graphite. If it is a mixture of metal and glass, we have found 50% metal, 50% glass to be satisiactory. The glass is crushed to pass a mesh screen, and is mixed thoroughly with the filler and a suitable binder such as hydrogenated cotton seed oil, commercially known as Dritex. This mixture may be formed into cylindrical pellets under pressure. Glass seals of this type are described in Patent 2,106,578 to Karl Schwartzwalder et al., issued January 25, 1938, Patent 2,071,571 to Hector Rabezzana et al., issued February 23, 1937, and patent application Serial No. 34:3,808 of Karl Schwartzwalder et al., filed July 3, 1940.

The assembly shown in Figu'e 1 is next heated to a temperature of 1650 F. or higher to make the glass plastic. Pressure is then applied to screw i8 to force it into the desired position. shown in Figure 2. This pressure causes pellet 23 to flow and react with insulator n and pilot wire 22. The condition of pellet 23 after fiowing under pressure is indicated at 23a in Figure 2.

seali'ng material 24 is likewise caused to flow between screw s and the insulator, as shown at ua ot Figure 2. I After the assembly has cooled. a compression or vacuum tight seal exists between electrode N and insulator o. and the whole structure is held rigidly together so that no compression leakage occurs even after the most severe usage.

We claim:

1. Aceramic body having a passageway therethrough, a recessed terminal in said passageway, a conductor in the passageway and in contact with the terminal through its recesses, said conductor having a low coeflicient of thermal expansion, a fluid-tight seal of hard class bonded to the conductor and the ceramic body, and a glass seal of greater plasticlty than the first glass seal between the insulator and the terminal.

2. A ceramic body with an opening therethrough, an enlargement in said opening deflning a shoulder, an electrode in the opening having a relatively high coemcient of thermal expansion, a flange on the electrode abutting on the shoulder, a wire having a low co'eflicient of thermal expansion Joined to the electrode, a recessed ter- 25 minal in the enlargement having contact in its recess with the wire, a fluid-tight seal oi! hard glass bonded to the wire and the ceramic body, and a second seal between the terminal and ceramic body, said second seal including` glass having greateplasticity than the first glas& seal.

3. In a spari: plug. an insulator having an opening therethrough, a terminal in said opening. an elongated recess in said terminal, a wire in said opening and in contact with the terminal at the inner end of said recess, a fluid ti'ght seal having a bonded connection to the wire and the insulator, and a second seal between the insulator and the terminal. i

4. In a spark plug, a ceramic insulator having an opening therethrough, a terminal in said opening, an electrode in said opening having a relatively high coeflicient of thermal expansion, a

,conductor having a low coemcient of thermal expansion Joined at one of its ends to said electrode and having its other end in electrical conducting relationship with the terminal, a fluidtight seal of hard siass bonded to the conductor and to the ceramic insulator, said hard glass having substantiaiv the same coemcient of thermal expansion as said conductor, and a second seal between the insulator and the terminal, said second seal including glass having a greater plasticity than the hard glass seal.

KARLSCHWAR'IZWAIDER. ROBERT W. SMITH.

cmw cm OF conmzcnon. v Patento. 2517505. April 20, 1915.

KARL SCBWARTMIDER, ET AL.

I t is hareby certified tlnt error appears in the printed. spcification of the above mmbered patent requirng correction as rollowa: Page 2, first columh, line 13, claim l, for "reesses" read --recess--; and that the said Letters Patet should be read with ths correction theren that the same `may oonfom to the record of the case in the Patent Office.

signed and sealed this lst day or June, A. 13.491&

Hear& Van Arsdae (Seal)` Acting commissoner of Patents.

CERTIFICATE OF comcmox. Patento. 2,37,3o5. April 20, 1915.

KARL SCHWARTZWAIDER, ET AL.

I t s hereby certified that eri-gr appears in the printed spcfcation of the abof numbered patent requirng correction as follows: Page 2, first colum n, line 13, clim l, for "reesaes" read --recess--; and that the said Letters Patent should be read with this correction ther-ein that the same `may conform to the record of the case in the Patent office.

Signed and sealed ths let day of June, A. 131915.

Henry Van Arsdae (8631)* Acting commasoner or Patents. 

